Post lab 5:

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1. What fraction of energy will be lost when a moving cart of mass m inelastically collides with a stationary cart of mass ? 2m?

2. Why do we choose to measure the velocity as close to the collision as we can? What would happen if we measured the velocity several seconds afterwards?

3. How much more energy does a car going at 60 mph have compared to a car going at 30 mph?

4. One rubber ball and one mud ball travel towards a wall with the same velocity. The rubber ball bounces off with the same speed and the mud ball sticks. Which one is the elastic collision and which ones is the inelastic collision? Which ball transfers more momentum to the wall? how much and why? Balls have the same mass.

5. Imagine an elastic collision between two gliders. One glider has really large mass and some initial velocity vi, the other a very small mass and no initial velocity (m1>>m2). What should the final velocities of the gliders be respectively? (Hint: Try looking at the derived formulas and think about a semi-truck hitting a marble and make some appropriate approximations to simplify those equations.) Show your work.

6. A ball of mass 100g is dropped from a height H=2m above the floor. It rebounds vertically to a height h=1.5 m after the colliding with the floor. Find the momentum of the ball immediately before and after the ball collides with the floor. Find the coefficient of restitution and determine the type of collision. Show your work.

7. Let's say I am in a bumper car and have a velocity of 14 m/s, driving North. I and my car have a mass of 120 kg. You are in a bumper car, sitting still. I run into you, and we collide elastically. If I end up with a velocity of 2 m/s going South, am I heaver or lighter than you? What is your mass, and what is your final velocity? Show your work.

Prelab 6:

Please write dawn the detail of your calculation, not just the final result.

1. What are the two necessary conditions for objects in translational and rotational equilibrium? τ is torque on the object(s), F is the force on the object(s), v is the translational velocity of the object(s), and ω is the angular velocity of the object(s).

a. Σ τ = 0

b. Σ F = 0

c. Σ v = 0

d. Σ ω = 0

e. There is an additional condition not on the list above.

2. If I have a bar of length 2d that is supported on a peg at a distance 3/2d from the left end of the bar and I place a force of F in the downward direction at a point d/4 from the right end.

a. Is the resulting torque positive or negative?

b. What is magnitude of torque of force F?

c. What is the torque of the force (direction and magnitude) I need to add to the left END of the bar at 3d/4 to keep it in equilibrium?

3. If Hobbs is waiting for Calvin to come home from school and pounces on Calvin as he opens the door. Hobbs hits Calvin with a force of 50N on his head (1.2 meter above the ground) at an upward angle from horizontal of 15 degrees. What is the magnitude of the torque that Hobbs produces if we assume the axis of rotation is at Calvin’s feet?

4. How do we define the angle, theta, when we deal with Torque? (1) ie:

The angle, theta, is measured between _________________ and ___________________.

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